nasm/disasm/disasm.c

/* ----------------------------------------------------------------------- *
 *
 *   Copyright 1996-2022 The NASM Authors - All Rights Reserved
 *   See the file AUTHORS included with the NASM distribution for
 *   the specific copyright holders.
 *
 *   Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following
 *   conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above
 *     copyright notice, this list of conditions and the following
 *     disclaimer in the documentation and/or other materials provided
 *     with the distribution.
 *
 *     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 *     CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 *     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 *     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *     DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 *     CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *     SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *     NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 *     LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 *     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 *     CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 *     OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 *     EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ----------------------------------------------------------------------- */

/*
 * disasm.c   where all the _work_ gets done in the Netwide Disassembler
 *
 * See x86/bytecode.txt for the definition of the instruction encoding
 * byte codes.
 */

#include "compiler.h"


#include "nasm.h"
#include "disasm.h"
#include "sync.h"
#include "insns.h"
#include "tables.h"
#include "regdis.h"
#include "disp8.h"

#define fetch_safe(_start, _ptr, _size, _need, _op)         \
    do {                                                    \
        if (((_ptr) - (_start)) >= ((_size) - (_need)))     \
            _op;                                            \
    } while (0)

#define fetch_or_return(_start, _ptr, _size, _need)         \
    fetch_safe(_start, _ptr, _size, _need, return 0)

/*
 * Flags that go into the `segment' field of `insn' structures
 * during disassembly.
 */
#define SEG_RELATIVE    1
#define SEG_32BIT       2
#define SEG_RMREG       4
#define SEG_DISP8       8
#define SEG_DISP16     16
#define SEG_DISP32     32
#define SEG_NODISP     64
#define SEG_SIGNED    128
#define SEG_64BIT     256

/*
 * Prefix information
 */
struct prefix_info {
    uint8_t osize;      /* Operand size */
    uint8_t asize;      /* Address size */
    uint8_t osp;        /* Operand size prefix present */
    uint8_t asp;        /* Address size prefix present */
    uint8_t rep;        /* Rep prefix present */
    uint8_t seg;        /* Segment override prefix present */
    uint8_t wait;       /* WAIT "prefix" present */
    uint8_t lock;       /* Lock prefix present */
    uint8_t vex[3];     /* VEX prefix present */
    uint8_t vex_c;      /* VEX "class" (VEX, XOP, ...) */
    uint8_t vex_m;      /* VEX.M field */
    uint8_t vex_v;
    uint8_t vex_lp;     /* VEX.LP fields */
    uint32_t rex;       /* REX prefix present */
    uint8_t evex[3];    /* EVEX prefix present */
};

#define getu8(x) (*(uint8_t *)(x))
#if X86_MEMORY
/* Littleendian CPU which can handle unaligned references */
#define getu16(x) (*(uint16_t *)(x))
#define getu32(x) (*(uint32_t *)(x))
#define getu64(x) (*(uint64_t *)(x))
#else
static uint16_t getu16(uint8_t *data)
{
    return (uint16_t)data[0] + ((uint16_t)data[1] << 8);
}
static uint32_t getu32(uint8_t *data)
{
    return (uint32_t)getu16(data) + ((uint32_t)getu16(data+2) << 16);
}
static uint64_t getu64(uint8_t *data)
{
    return (uint64_t)getu32(data) + ((uint64_t)getu32(data+4) << 32);
}
#endif

#define gets8(x) ((int8_t)getu8(x))
#define gets16(x) ((int16_t)getu16(x))
#define gets32(x) ((int32_t)getu32(x))
#define gets64(x) ((int64_t)getu64(x))

/* Important: regval must already have been adjusted for rex extensions */
static enum reg_enum whichreg(opflags_t regflags, int regval, int rex)
{
    size_t i;

    static const struct {
        opflags_t       flags;
        enum reg_enum   reg;
    } specific_registers[] = {
        {REG_AL,  R_AL},
        {REG_AX,  R_AX},
        {REG_EAX, R_EAX},
        {REG_RAX, R_RAX},
        {REG_DL,  R_DL},
        {REG_DX,  R_DX},
        {REG_EDX, R_EDX},
        {REG_RDX, R_RDX},
        {REG_CL,  R_CL},
        {REG_CX,  R_CX},
        {REG_ECX, R_ECX},
        {REG_RCX, R_RCX},
        {FPU0,    R_ST0},
        {XMM0,    R_XMM0},
        {YMM0,    R_YMM0},
        {ZMM0,    R_ZMM0},
        {REG_ES,  R_ES},
        {REG_CS,  R_CS},
        {REG_SS,  R_SS},
        {REG_DS,  R_DS},
        {REG_FS,  R_FS},
        {REG_GS,  R_GS},
        {OPMASK0, R_K0},
    };

    if (!(regflags & (REGISTER|REGMEM)))
        return 0;        /* Registers not permissible?! */

    regflags |= REGISTER;

    for (i = 0; i < ARRAY_SIZE(specific_registers); i++)
        if (!(specific_registers[i].flags & ~regflags))
            return specific_registers[i].reg;

    /* All the entries below look up regval in an 16-entry array */
    if (regval < 0 || regval > (rex & REX_EV ? 31 : 15))
        return 0;

#define GET_REGISTER(__array, __index)                      \
    ((size_t)(__index) < (size_t)ARRAY_SIZE(__array) ? __array[(__index)] : 0)

    if (!(REG8 & ~regflags)) {
        if (rex & (REX_P|REX_NH))
            return GET_REGISTER(nasm_rd_reg8_rex, regval);
        else
            return GET_REGISTER(nasm_rd_reg8, regval);
    }
    if (!(REG16 & ~regflags))
        return GET_REGISTER(nasm_rd_reg16, regval);
    if (!(REG32 & ~regflags))
        return GET_REGISTER(nasm_rd_reg32, regval);
    if (!(REG64 & ~regflags))
        return GET_REGISTER(nasm_rd_reg64, regval);
    if (!(REG_SREG & ~regflags))
        return GET_REGISTER(nasm_rd_sreg, regval & 7); /* Ignore REX */
    if (!(REG_CREG & ~regflags))
        return GET_REGISTER(nasm_rd_creg, regval);
    if (!(REG_DREG & ~regflags))
        return GET_REGISTER(nasm_rd_dreg, regval);
    if (!(REG_TREG & ~regflags)) {
        if (regval > 7)
            return 0;        /* TR registers are ill-defined with rex */
        return GET_REGISTER(nasm_rd_treg, regval);
    }
    if (!(FPUREG & ~regflags))
        return GET_REGISTER(nasm_rd_fpureg, regval & 7); /* Ignore REX */
    if (!(MMXREG & ~regflags))
        return GET_REGISTER(nasm_rd_mmxreg, regval & 7); /* Ignore REX */
    if (!(XMMREG & ~regflags))
        return GET_REGISTER(nasm_rd_xmmreg, regval);
    if (!(YMMREG & ~regflags))
        return GET_REGISTER(nasm_rd_ymmreg, regval);
    if (!(ZMMREG & ~regflags))
        return GET_REGISTER(nasm_rd_zmmreg, regval);
    if (!(OPMASKREG & ~regflags))
        return GET_REGISTER(nasm_rd_opmaskreg, regval);
    if (!(BNDREG & ~regflags))
        return GET_REGISTER(nasm_rd_bndreg, regval);
    if (!(TMMREG & ~regflags))
        return GET_REGISTER(nasm_rd_tmmreg, regval);

#undef GET_REGISTER
    return 0;
}

static uint32_t append_evex_reg_deco(char *buf, uint32_t num,
                                    decoflags_t deco, uint8_t *evex)
{
    const char * const er_names[] = {"rn-sae", "rd-sae", "ru-sae", "rz-sae"};
    uint32_t num_chars = 0;

    if ((deco & MASK) && (evex[2] & EVEX_P2AAA)) {
        enum reg_enum opmasknum = nasm_rd_opmaskreg[evex[2] & EVEX_P2AAA];
        const char * regname = nasm_reg_names[opmasknum - EXPR_REG_START];

        num_chars += snprintf(buf + num_chars, num - num_chars,
                              "{%s}", regname);

        if ((deco & Z) && (evex[2] & EVEX_P2Z)) {
            num_chars += snprintf(buf + num_chars, num - num_chars,
                                  "{z}");
        }
    }

    if (evex[2] & EVEX_P2B) {
        if (deco & ER) {
            uint8_t er_type = (evex[2] & EVEX_P2LL) >> 5;
            num_chars += snprintf(buf + num_chars, num - num_chars,
                                  ",{%s}", er_names[er_type]);
        } else if (deco & SAE) {
            num_chars += snprintf(buf + num_chars, num - num_chars,
                                  ",{sae}");
        }
    }

    return num_chars;
}

static uint32_t append_evex_mem_deco(char *buf, uint32_t num, opflags_t type,
                                     decoflags_t deco, uint8_t *evex)
{
    uint32_t num_chars = 0;

    if ((evex[2] & EVEX_P2B) && (deco & BRDCAST_MASK)) {
        decoflags_t deco_brsize = deco & BRSIZE_MASK;
        opflags_t template_opsize = brsize_to_size(deco_brsize);
        unsigned int br_num = (type & SIZE_MASK) / BITS128 *
            BITS64 / template_opsize * 2;

        num_chars += snprintf(buf + num_chars, num - num_chars,
                              "{1to%d}", br_num);
    }

    if ((deco & MASK) && (evex[2] & EVEX_P2AAA)) {
        enum reg_enum opmasknum = nasm_rd_opmaskreg[evex[2] & EVEX_P2AAA];
        const char * regname = nasm_reg_names[opmasknum - EXPR_REG_START];

        num_chars += snprintf(buf + num_chars, num - num_chars,
                              "{%s}", regname);

        if ((deco & Z) && (evex[2] & EVEX_P2Z)) {
            num_chars += snprintf(buf + num_chars, num - num_chars,
                                  "{z}");
        }
    }


    return num_chars;
}

/*
 * Process an effective address (ModRM) specification.
 */
static uint8_t *do_ea(uint8_t *data, int modrm, int asize,
                      int segsize, enum ea_type type,
                      operand *op, insn *ins)
{
    int mod, rm, scale, index, base;
    int rex;
    uint8_t *evex;
    uint8_t sib = 0;
    bool is_evex = !!(ins->rex & REX_EV);

    mod = (modrm >> 6) & 03;
    rm = modrm & 07;

    if (mod != 3 && asize != 16 && rm == 4)
        sib = *data++;

    rex  = ins->rex;
    evex = ins->evex_p;

    if (mod == 3) {             /* pure register version */
        op->basereg = rm+(rex & REX_B ? 8 : 0);
        op->segment |= SEG_RMREG;
        if (is_evex && segsize == 64) {
            op->basereg += (evex[0] & EVEX_P0X ? 0 : 16);
        }
        return data;
    }

    op->disp_size = 0;
    op->eaflags = 0;

    if (asize == 16) {
        /*
         * <mod> specifies the displacement size (none, byte or
         * word), and <rm> specifies the register combination.
         * Exception: mod=0,rm=6 does not specify [BP] as one might
         * expect, but instead specifies [disp16].
         */

        if (type != EA_SCALAR)
            return NULL;

        op->indexreg = op->basereg = -1;
        op->scale = 1;          /* always, in 16 bits */
        switch (rm) {
        case 0:
            op->basereg = R_BX;
            op->indexreg = R_SI;
            break;
        case 1:
            op->basereg = R_BX;
            op->indexreg = R_DI;
            break;
        case 2:
            op->basereg = R_BP;
            op->indexreg = R_SI;
            break;
        case 3:
            op->basereg = R_BP;
            op->indexreg = R_DI;
            break;
        case 4:
            op->basereg = R_SI;
            break;
        case 5:
            op->basereg = R_DI;
            break;
        case 6:
            op->basereg = R_BP;
            break;
        case 7:
            op->basereg = R_BX;
            break;
        }
        if (rm == 6 && mod == 0) {      /* special case */
            op->basereg = -1;
            if (segsize != 16)
                op->disp_size = 16;
            mod = 2;            /* fake disp16 */
        }
        switch (mod) {
        case 0:
            op->segment |= SEG_NODISP;
            break;
        case 1:
            op->segment |= SEG_DISP8;
            if (ins->evex_tuple != 0) {
                op->offset = gets8(data) * get_disp8N(ins);
            } else {
                op->offset = gets8(data);
            }
            data++;
            break;
        case 2:
            op->segment |= SEG_DISP16;
            op->offset = *data++;
            op->offset |= ((unsigned)*data++) << 8;
            break;
        }
        return data;
    } else {
        /*
         * Once again, <mod> specifies displacement size (this time
         * none, byte or *dword*), while <rm> specifies the base
         * register. Again, [EBP] is missing, replaced by a pure
         * disp32 (this time that's mod=0,rm=*5*) in 32-bit mode,
         * and RIP-relative addressing in 64-bit mode.
         *
         * However, rm=4
         * indicates not a single base register, but instead the
         * presence of a SIB byte...
         */
        int a64 = asize == 64;

        op->indexreg = -1;

        if (a64)
            op->basereg = nasm_rd_reg64[rm | ((rex & REX_B) ? 8 : 0)];
        else
            op->basereg = nasm_rd_reg32[rm | ((rex & REX_B) ? 8 : 0)];

        if (rm == 5 && mod == 0) {
            if (segsize == 64) {
                op->eaflags |= EAF_REL;
                op->segment |= SEG_RELATIVE;
            }

            if (asize != 64)
                op->disp_size = asize;

            op->basereg = -1;
            mod = 2;            /* fake disp32 */
        }


        if (rm == 4) {          /* process SIB */
            uint8_t vsib_hi = 0;
            scale = (sib >> 6) & 03;
            index = (sib >> 3) & 07;
            base = sib & 07;

            op->scale = 1 << scale;

            if (segsize == 64) {
                vsib_hi = (rex & REX_X ? 8 : 0) |
                          (evex[2] & EVEX_P2VP ? 0 : 16);
            }

            if (type == EA_XMMVSIB)
                op->indexreg = nasm_rd_xmmreg[index | vsib_hi];
            else if (type == EA_YMMVSIB)
                op->indexreg = nasm_rd_ymmreg[index | vsib_hi];
            else if (type == EA_ZMMVSIB)
                op->indexreg = nasm_rd_zmmreg[index | vsib_hi];
            else if (index == 4 && !(rex & REX_X))
                op->indexreg = -1; /* ESP/RSP cannot be an index */
            else if (a64)
                op->indexreg = nasm_rd_reg64[index | ((rex & REX_X) ? 8 : 0)];
            else
                op->indexreg = nasm_rd_reg32[index | ((rex & REX_X) ? 8 : 0)];

            if (base == 5 && mod == 0) {
                op->basereg = -1;
                mod = 2;    /* Fake disp32 */
            } else if (a64)
                op->basereg = nasm_rd_reg64[base | ((rex & REX_B) ? 8 : 0)];
            else
                op->basereg = nasm_rd_reg32[base | ((rex & REX_B) ? 8 : 0)];

            if (segsize == 16)
                op->disp_size = 32;
        } else if (type != EA_SCALAR) {
            /* Can't have VSIB without SIB */
            return NULL;
        }

        switch (mod) {
        case 0:
            op->segment |= SEG_NODISP;
            break;
        case 1:
            op->segment |= SEG_DISP8;
            if (ins->evex_tuple != 0) {
                op->offset = gets8(data) * get_disp8N(ins);
            } else {
                op->offset = gets8(data);
            }
            data++;
            break;
        case 2:
            op->segment |= SEG_DISP32;
            op->offset = gets32(data);
            data += 4;
            break;
        }
        return data;
    }
}

/*
 * Determine whether the instruction template in t corresponds to the data
 * stream in data. Return the number of bytes matched if so.
 */
#define case4(x) case (x): case (x)+1: case (x)+2: case (x)+3

static int matches(const struct itemplate *t, uint8_t *data,
                   const struct prefix_info *prefix, int segsize, insn *ins)
{
    uint8_t *r = (uint8_t *)(t->code);
    uint8_t *origdata = data;
    bool a_used = false, o_used = false;
    enum prefixes drep = 0;
    enum prefixes dwait = 0;
    uint8_t lock = prefix->lock;
    int osize = prefix->osize;
    int asize = prefix->asize;
    int i, c;
    int op1, op2;
    struct operand *opx, *opy;
    uint8_t opex = 0;
    bool vex_ok = false;
    int regmask = (segsize == 64) ? 15 : 7;
    enum ea_type eat = EA_SCALAR;

    for (i = 0; i < MAX_OPERANDS; i++) {
        ins->oprs[i].segment = ins->oprs[i].disp_size =
            (segsize == 64 ? SEG_64BIT : segsize == 32 ? SEG_32BIT : 0);
    }
    ins->evex_tuple = 0;
    ins->rex = prefix->rex;
    memset(ins->prefixes, 0, sizeof ins->prefixes);

    if (itemp_has(t, (segsize == 64 ? IF_NOLONG : IF_LONG)))
        return 0;

    if (prefix->rep == 0xF2)
        drep = (itemp_has(t, IF_BND) ? P_BND : P_REPNE);
    else if (prefix->rep == 0xF3)
        drep = P_REP;

    dwait = prefix->wait ? P_WAIT : 0;

    while ((c = *r++) != 0) {
        op1 = (c & 3) + ((opex & 1) << 2);
        op2 = ((c >> 3) & 3) + ((opex & 2) << 1);
        opx = &ins->oprs[op1];
        opy = &ins->oprs[op2];
        opex = 0;

        switch (c) {
        case 01:
        case 02:
        case 03:
        case 04:
            while (c--)
                if (*r++ != *data++)
                    return 0;
            break;

        case 05:
        case 06:
        case 07:
            opex = c;
            break;

        case4(010):
        {
            int t = *r++, d = *data++;
            if (d < t || d > t + 7)
                return 0;
            else {
                opx->basereg = (d-t)+
                    (ins->rex & REX_B ? 8 : 0);
                opx->segment |= SEG_RMREG;
            }
            break;
        }

        case4(014):
            /* this is an separate index reg position of MIB operand (ICC) */
            /* Disassembler uses NASM's split EA form only                 */
            break;

        case4(0274):
            opx->offset = (int8_t)*data++;
            opx->segment |= SEG_SIGNED;
            break;

        case4(020):
            opx->offset = *data++;
            break;

        case4(024):
            opx->offset = *data++;
            break;

        case4(030):
            opx->offset = getu16(data);
            data += 2;
            break;

        case4(034):
            if (osize == 32) {
                opx->offset = getu32(data);
                data += 4;
            } else {
                opx->offset = getu16(data);
                data += 2;
            }
            if (segsize != asize)
                opx->disp_size = asize;
            break;

        case4(040):
            opx->offset = getu32(data);
            data += 4;
            break;

        case4(0254):
            opx->offset = gets32(data);
            data += 4;
            break;

        case4(044):
            switch (asize) {
            case 16:
                opx->offset = getu16(data);
                data += 2;
                if (segsize != 16)
                    opx->disp_size = 16;
                break;
            case 32:
                opx->offset = getu32(data);
                data += 4;
                if (segsize == 16)
                    opx->disp_size = 32;
                break;
            case 64:
                opx->offset = getu64(data);
                opx->disp_size = 64;
                data += 8;
                break;
            }
            break;

        case4(050):
            opx->offset = gets8(data++);
            opx->segment |= SEG_RELATIVE;
            break;

        case4(054):
            opx->offset = getu64(data);
            data += 8;
            break;

        case4(060):
            opx->offset = gets16(data);
            data += 2;
            opx->segment |= SEG_RELATIVE;
            opx->segment &= ~SEG_32BIT;
            break;

        case4(064):  /* rel */
            opx->segment |= SEG_RELATIVE;
            /* In long mode rel is always 32 bits, sign extended. */
            if (segsize == 64 || osize == 32) {
                opx->offset = gets32(data);
                data += 4;
                if (segsize != 64)
                    opx->segment |= SEG_32BIT;
                opx->type = (opx->type & ~SIZE_MASK)
                    | (segsize == 64 ? BITS64 : BITS32);
            } else {
                opx->offset = gets16(data);
                data += 2;
                opx->segment &= ~SEG_32BIT;
                opx->type = (opx->type & ~SIZE_MASK) | BITS16;
            }
            break;

        case4(070):
            opx->offset = gets32(data);
            data += 4;
            opx->segment |= SEG_32BIT | SEG_RELATIVE;
            break;

        case4(0100):
        case4(0110):
        case4(0120):
        case4(0130):
        {
            int modrm = *data++;
            opx->segment |= SEG_RMREG;
            data = do_ea(data, modrm, asize, segsize, eat, opy, ins);
            if (!data)
                return 0;
            opx->basereg = ((modrm >> 3) & 7) + (ins->rex & REX_R ? 8 : 0);
            if ((ins->rex & REX_EV) && (segsize == 64))
                opx->basereg += (ins->evex_p[0] & EVEX_P0RP ? 0 : 16);
            break;
        }

        case 0171:
        {
            uint8_t t = *r++;
            uint8_t d = *data++;
            if ((d ^ t) & ~070) {
                return 0;
            } else {
                op2 = (op2 & ~3) | ((t >> 3) & 3);
                opy = &ins->oprs[op2];
                opy->basereg = ((d >> 3) & 7) +
                    (ins->rex & REX_R ? 8 : 0);
                opy->segment |= SEG_RMREG;
            }
            break;
        }

        case 0172:
            {
                uint8_t ximm = *data++;
                c = *r++;
                ins->oprs[c >> 3].basereg = (ximm >> 4) & regmask;
                ins->oprs[c >> 3].segment |= SEG_RMREG;
                ins->oprs[c & 7].offset = ximm & 15;
            }
            break;

        case 0173:
            {
                uint8_t ximm = *data++;
                c = *r++;

                if ((c ^ ximm) & 15)
                    return 0;

                ins->oprs[c >> 4].basereg = (ximm >> 4) & regmask;
                ins->oprs[c >> 4].segment |= SEG_RMREG;
            }
            break;

        case4(0174):
            {
                uint8_t ximm = *data++;

                opx->basereg = (ximm >> 4) & regmask;
                opx->segment |= SEG_RMREG;
            }
            break;

        case4(0200):
        case4(0204):
        case4(0210):
        case4(0214):
        case4(0220):
        case4(0224):
        case4(0230):
        case4(0234):
        {
            int modrm = *data++;
            if (((modrm >> 3) & 07) != (c & 07))
                return 0;   /* spare field doesn't match up */
            data = do_ea(data, modrm, asize, segsize, eat, opy, ins);
            if (!data)
                return 0;
            break;
        }

        case4(0240):
        case 0250:
        {
            uint8_t evexm   = *r++;
            uint8_t evexwlp = *r++;
            uint8_t modrm, valid_mask;
            ins->evex_tuple = *r++ - 0300;
            modrm = *(origdata + 1);

            ins->rex |= REX_EV;
            if ((prefix->rex & (REX_EV|REX_V|REX_P)) != REX_EV)
                return 0;

            if ((evexm & 0x1f) != prefix->vex_m)
                return 0;

            switch (evexwlp & 060) {
            case 000:
                if (prefix->rex & REX_W)
                    return 0;
                break;
            case 020:
                if (!(prefix->rex & REX_W))
                    return 0;
                ins->rex |= REX_W;
                break;
            case 040:        /* VEX.W is a don't care */
                ins->rex &= ~REX_W;
                break;
            case 060:
                break;
            }

            /* If EVEX.b is set with reg-reg op,
             * EVEX.L'L contains embedded rounding control info
             */
            if ((prefix->evex[2] & EVEX_P2B) && ((modrm >> 6) == 3)) {
                valid_mask = 0x3;   /* prefix only */
            } else {
                valid_mask = 0xf;   /* vector length and prefix */
            }
            if ((evexwlp ^ prefix->vex_lp) & valid_mask)
                return 0;

            if (c == 0250) {
                if ((prefix->vex_v != 0) ||
                    (!(prefix->evex[2] & EVEX_P2VP) &&
                     ((eat < EA_XMMVSIB) || (eat > EA_ZMMVSIB))))
                    return 0;
            } else {
                opx->segment |= SEG_RMREG;
                opx->basereg = ((~prefix->evex[2] & EVEX_P2VP) << (4 - 3) ) |
                                prefix->vex_v;
            }
            vex_ok = true;
            memcpy(ins->evex_p, prefix->evex, 3);
            break;
        }

        case4(0260):
        case 0270:
        {
            int vexm   = *r++;
            int vexwlp = *r++;

            ins->rex |= REX_V;
            if ((prefix->rex & (REX_V|REX_P)) != REX_V)
                return 0;

            if ((vexm & 0x1f) != prefix->vex_m)
                return 0;

            switch (vexwlp & 060) {
            case 000:
                if (prefix->rex & REX_W)
                    return 0;
                break;
            case 020:
                if (!(prefix->rex & REX_W))
                    return 0;
                ins->rex &= ~REX_W;
                break;
            case 040:        /* VEX.W is a don't care */
                ins->rex &= ~REX_W;
                break;
            case 060:
                break;
            }

            /* The 010 bit of vexwlp is set if VEX.L is ignored */
            if ((vexwlp ^ prefix->vex_lp) & ((vexwlp & 010) ? 03 : 07))
                return 0;

            if (c == 0270) {
                if (prefix->vex_v != 0)
                    return 0;
            } else {
                opx->segment |= SEG_RMREG;
                opx->basereg = prefix->vex_v;
            }
            vex_ok = true;
            break;
        }

        case 0271:
            if (prefix->rep == 0xF3)
                drep = P_XRELEASE;
            break;

        case 0272:
            if (prefix->rep == 0xF2)
                drep = P_XACQUIRE;
            else if (prefix->rep == 0xF3)
                drep = P_XRELEASE;
            break;

        case 0273:
            if (prefix->lock == 0xF0) {
                if (prefix->rep == 0xF2)
                    drep = P_XACQUIRE;
                else if (prefix->rep == 0xF3)
                    drep = P_XRELEASE;
            }
            break;

        case 0310:
            if (asize != 16)
                return 0;
            else
                a_used = true;
            break;

        case 0311:
            if (asize != 32)
                return 0;
            else
                a_used = true;
            break;

        case 0312:
            if (asize != segsize)
                return 0;
            else
                a_used = true;
            break;

        case 0313:
            if (asize != 64)
                return 0;
            else
                a_used = true;
            break;

        case 0314:
            if (prefix->rex & REX_B)
                return 0;
            break;

        case 0315:
            if (prefix->rex & REX_X)
                return 0;
            break;

        case 0316:
            if (prefix->rex & REX_R)
                return 0;
            break;

        case 0317:
            if (prefix->rex & REX_W)
                return 0;
            break;

        case 0320:
            if (osize != 16)
                return 0;
            else
                o_used = true;
            break;

        case 0321:
            if (osize != 32)
                return 0;
            else
                o_used = true;
            break;

        case 0322:
            if (osize != (segsize == 16 ? 16 : 32))
                return 0;
            else
                o_used = true;
            break;

        case 0323:
            ins->rex |= REX_W;    /* 64-bit only instruction */
            osize = 64;
            o_used = true;
            break;

        case 0324:
            if (osize != 64)
                return 0;
            o_used = true;
            break;

        case 0325:
            ins->rex |= REX_NH;
            break;

        case 0326:
            if (prefix->rep == 0xF3)
                return 0;
            break;

        case 0331:
            if (prefix->rep)
                return 0;
            break;

        case 0332:
            if (prefix->rep != 0xF2)
                return 0;
            drep = 0;
            break;

        case 0333:
            if (prefix->rep != 0xF3)
                return 0;
            drep = 0;
            break;

        case 0334:
            if (lock) {
                ins->rex |= REX_R;
                lock = 0;
            }
            break;

        case 0335:
            if (drep == P_REP)
                drep = P_REPE;
            break;

        case 0336:
        case 0337:
            break;

        case 0340:
            return 0;

        case 0341:
            if (prefix->wait != 0x9B)
                return 0;
            dwait = 0;
            break;

        case 0360:
            if (prefix->osp || prefix->rep)
                return 0;
            break;

        case 0361:
            if (!prefix->osp || prefix->rep)
                return 0;
            o_used = true;
            break;

        case 0364:
            if (prefix->osp)
                return 0;
            break;

        case 0365:
            if (prefix->asp)
                return 0;
            break;

        case 0366:
            if (!prefix->osp)
                return 0;
            o_used = true;
            break;

        case 0367:
            if (!prefix->asp)
                return 0;
            a_used = true;
            break;

        case 0370:
        case 0371:
            break;

        case 0374:
            eat = EA_XMMVSIB;
            break;

        case 0375:
            eat = EA_YMMVSIB;
            break;

        case 0376:
            eat = EA_ZMMVSIB;
            break;

        default:
            return 0;    /* Unknown code */
        }
    }

    if (!vex_ok && (ins->rex & (REX_V | REX_EV)))
        return 0;

    /* REX cannot be combined with VEX */
    if ((ins->rex & REX_V) && (prefix->rex & REX_P))
        return 0;

    /*
     * Check for unused rep or a/o prefixes.
     */
    for (i = 0; i < t->operands; i++) {
        if (ins->oprs[i].segment != SEG_RMREG)
            a_used = true;
    }

    if (lock) {
        if (ins->prefixes[PPS_LOCK])
            return 0;
        ins->prefixes[PPS_LOCK] = P_LOCK;
    }
    if (drep) {
        if (ins->prefixes[PPS_REP])
            return 0;
        ins->prefixes[PPS_REP] = drep;
    }
    ins->prefixes[PPS_WAIT] = dwait;
    if (!o_used) {
        if (osize != ((segsize == 16) ? 16 : 32)) {
            enum prefixes pfx = 0;

            switch (osize) {
            case 16:
                pfx = P_O16;
                break;
            case 32:
                pfx = P_O32;
                break;
            case 64:
                pfx = P_O64;
                break;
            }

            if (ins->prefixes[PPS_OSIZE])
                return 0;
            ins->prefixes[PPS_OSIZE] = pfx;
        }
    }
    if (!a_used && asize != segsize) {
        if (ins->prefixes[PPS_ASIZE])
            return 0;
        ins->prefixes[PPS_ASIZE] = asize == 16 ? P_A16 : P_A32;
    }

    /* Fix: check for redundant REX prefixes */

    return data - origdata;
}

int32_t disasm(uint8_t *data, int32_t data_size, char *output, int outbufsize, int segsize,
               int64_t offset, int autosync, iflag_t *prefer)
{
    const struct itemplate * const *p, * const *best_p;
    const struct disasm_index *ix;
    uint8_t *dp;
    int length, best_length = 0;
    char *segover;
    int i, slen, colon, n;
    uint8_t *origdata;
    int works;
    insn tmp_ins, ins;
    iflag_t goodness, best;
    int best_pref;
    struct prefix_info prefix;
    bool end_prefix;
    bool is_evex;

    memset(&ins, 0, sizeof ins);

    /*
     * Scan for prefixes.
     */
    memset(&prefix, 0, sizeof prefix);
    prefix.asize = segsize;
    prefix.osize = (segsize == 64) ? 32 : segsize;
    segover = NULL;
    origdata = data;

    ix = itable;

    end_prefix = false;
    while (!end_prefix) {
        switch (*data) {
        case 0xF2:
        case 0xF3:
            fetch_or_return(origdata, data, data_size, 1);
            prefix.rep = *data++;
            break;

        case 0x9B:
            fetch_or_return(origdata, data, data_size, 1);
            prefix.wait = *data++;
            break;

        case 0xF0:
            fetch_or_return(origdata, data, data_size, 1);
            prefix.lock = *data++;
            break;

        case 0x2E:
            fetch_or_return(origdata, data, data_size, 1);
            segover = "cs", prefix.seg = *data++;
            break;
        case 0x36:
            fetch_or_return(origdata, data, data_size, 1);
            segover = "ss", prefix.seg = *data++;
            break;
        case 0x3E:
            fetch_or_return(origdata, data, data_size, 1);
            segover = "ds", prefix.seg = *data++;
            break;
        case 0x26:
            fetch_or_return(origdata, data, data_size, 1);
            segover = "es", prefix.seg = *data++;
            break;
        case 0x64:
            fetch_or_return(origdata, data, data_size, 1);
            segover = "fs", prefix.seg = *data++;
            break;
        case 0x65:
            fetch_or_return(origdata, data, data_size, 1);
            segover = "gs", prefix.seg = *data++;
            break;

        case 0x66:
            fetch_or_return(origdata, data, data_size, 1);
            prefix.osize = (segsize == 16) ? 32 : 16;
            prefix.osp = *data++;
            break;
        case 0x67:
            fetch_or_return(origdata, data, data_size, 1);
            prefix.asize = (segsize == 32) ? 16 : 32;
            prefix.asp = *data++;
            break;

        case 0xC4:
        case 0xC5:
            if (segsize == 64 || (data[1] & 0xc0) == 0xc0) {
                fetch_or_return(origdata, data, data_size, 2);
                prefix.vex[0] = *data++;
                prefix.vex[1] = *data++;

                prefix.rex = REX_V;
                prefix.vex_c = RV_VEX;

                if (prefix.vex[0] == 0xc4) {
                    fetch_or_return(origdata, data, data_size, 1);
                    prefix.vex[2] = *data++;
                    prefix.rex |= (~prefix.vex[1] >> 5) & 7; /* REX_RXB */
                    prefix.rex |= (prefix.vex[2] >> (7-3)) & REX_W;
                    prefix.vex_m = prefix.vex[1] & 0x1f;
                    prefix.vex_v = (~prefix.vex[2] >> 3) & 15;
                    prefix.vex_lp = prefix.vex[2] & 7;
                } else {
                    prefix.rex |= (~prefix.vex[1] >> (7-2)) & REX_R;
                    prefix.vex_m = 1;
                    prefix.vex_v = (~prefix.vex[1] >> 3) & 15;
                    prefix.vex_lp = prefix.vex[1] & 7;
                }

                ix = itable_vex[RV_VEX][prefix.vex_m][prefix.vex_lp & 3];
            }
            end_prefix = true;
            break;

        case 0x62:
        {
            if (segsize == 64 || ((data[1] & 0xc0) == 0xc0)) {
                fetch_or_return(origdata, data, data_size, 4);
                data++;        /* 62h EVEX prefix */
                prefix.evex[0] = *data++;
                prefix.evex[1] = *data++;
                prefix.evex[2] = *data++;

                prefix.rex    = REX_EV;
                prefix.vex_c  = RV_EVEX;
                prefix.rex   |= (~prefix.evex[0] >> 5) & 7; /* REX_RXB */
                prefix.rex   |= (prefix.evex[1] >> (7-3)) & REX_W;
                prefix.vex_m  = prefix.evex[0] & EVEX_P0MM;
                prefix.vex_v  = (~prefix.evex[1] & EVEX_P1VVVV) >> 3;
                prefix.vex_lp = ((prefix.evex[2] & EVEX_P2LL) >> (5-2)) |
                                (prefix.evex[1] & EVEX_P1PP);

                ix = itable_vex[prefix.vex_c][prefix.vex_m][prefix.vex_lp & 3];
            }
            end_prefix = true;
            break;
        }

        case 0x8F:
            if ((data[1] & 030) != 0 &&
                    (segsize == 64 || (data[1] & 0xc0) == 0xc0)) {
                fetch_or_return(origdata, data, data_size, 3);
                prefix.vex[0] = *data++;
                prefix.vex[1] = *data++;
                prefix.vex[2] = *data++;

                prefix.rex = REX_V;
                prefix.vex_c = RV_XOP;

                prefix.rex |= (~prefix.vex[1] >> 5) & 7; /* REX_RXB */
                prefix.rex |= (prefix.vex[2] >> (7-3)) & REX_W;
                prefix.vex_m = prefix.vex[1] & 0x1f;
                prefix.vex_v = (~prefix.vex[2] >> 3) & 15;
                prefix.vex_lp = prefix.vex[2] & 7;

                ix = itable_vex[RV_XOP][prefix.vex_m][prefix.vex_lp & 3];
            }
            end_prefix = true;
            break;

        case REX_P + 0x0:
        case REX_P + 0x1:
        case REX_P + 0x2:
        case REX_P + 0x3:
        case REX_P + 0x4:
        case REX_P + 0x5:
        case REX_P + 0x6:
        case REX_P + 0x7:
        case REX_P + 0x8:
        case REX_P + 0x9:
        case REX_P + 0xA:
        case REX_P + 0xB:
        case REX_P + 0xC:
        case REX_P + 0xD:
        case REX_P + 0xE:
        case REX_P + 0xF:
            if (segsize == 64) {
                fetch_or_return(origdata, data, data_size, 1);
                prefix.rex = *data++;
                if (prefix.rex & REX_W)
                    prefix.osize = 64;
            }
            end_prefix = true;
            break;

        default:
            end_prefix = true;
            break;
        }
    }

    iflag_set_all(&best); /* Worst possible */
    best_p = NULL;
    best_pref = INT_MAX;

    if (!ix)
        return 0;        /* No instruction table at all... */

    dp = data;
    fetch_or_return(origdata, dp, data_size, 1);
    ix += *dp++;
    while (ix->n == -1) {
        fetch_or_return(origdata, dp, data_size, 1);
        ix = (const struct disasm_index *)ix->p + *dp++;
    }

    p = (const struct itemplate * const *)ix->p;
    for (n = ix->n; n; n--, p++) {
        if ((length = matches(*p, data, &prefix, segsize, &tmp_ins))) {
            works = true;
            /*
             * Final check to make sure the types of r/m match up.
             * XXX: Need to make sure this is actually correct.
             */
            for (i = 0; i < (*p)->operands; i++) {
                if (
                        /* If it's a mem-only EA but we have a
                           register, die. */
                        ((tmp_ins.oprs[i].segment & SEG_RMREG) &&
                         is_class(MEMORY, (*p)->opd[i])) ||
                        /* If it's a reg-only EA but we have a memory
                           ref, die. */
                        (!(tmp_ins.oprs[i].segment & SEG_RMREG) &&
                         !(REG_EA & ~(*p)->opd[i]) &&
                         !((*p)->opd[i] & REG_SMASK)) ||
                        /* Register type mismatch (eg FS vs REG_DESS):
                           die. */
                        ((((*p)->opd[i] & (REGISTER | FPUREG)) ||
                          (tmp_ins.oprs[i].segment & SEG_RMREG)) &&
                         !whichreg((*p)->opd[i],
                             tmp_ins.oprs[i].basereg, tmp_ins.rex))
                   ) {
                    works = false;
                    break;
                }
            }

            /*
             * Note: we always prefer instructions which incorporate
             * prefixes in the instructions themselves.  This is to allow
             * e.g. PAUSE to be preferred to REP NOP, and deal with
             * MMX/SSE instructions where prefixes are used to select
             * between MMX and SSE register sets or outright opcode
             * selection.
             */
            if (works) {
                int i, nprefix;
                goodness = iflag_pfmask(*p);
                goodness = iflag_xor(&goodness, prefer);
		nprefix = 0;
		for (i = 0; i < MAXPREFIX; i++)
		    if (tmp_ins.prefixes[i])
			nprefix++;
                if (nprefix < best_pref ||
		    (nprefix == best_pref &&
                     iflag_cmp(&goodness, &best) < 0)) {
                    /* This is the best one found so far */
                    best = goodness;
                    best_p = p;
                    best_pref = nprefix;
                    best_length = length;
                    ins = tmp_ins;
                }
            }
        }
    }

    if (!best_p)
        return 0;               /* no instruction was matched */

    /* Pick the best match */
    p = best_p;
    length = best_length;

    slen = 0;

    /* TODO: snprintf returns the value that the string would have if
     *      the buffer were long enough, and not the actual length of
     *      the returned string, so each instance of using the return
     *      value of snprintf should actually be checked to assure that
     *      the return value is "sane."  Maybe a macro wrapper could
     *      be used for that purpose.
     */
    for (i = 0; i < MAXPREFIX; i++) {
        const char *prefix = prefix_name(ins.prefixes[i]);
        if (prefix)
            slen += snprintf(output+slen, outbufsize-slen, "%s ", prefix);
    }

    i = (*p)->opcode;
    slen += snprintf(output + slen, outbufsize - slen, "%s",
                     nasm_insn_names[i]);

    colon = false;
    is_evex = !!(ins.rex & REX_EV);
    length += data - origdata;  /* fix up for prefixes */
    for (i = 0; i < (*p)->operands; i++) {
        opflags_t t = (*p)->opd[i];
        decoflags_t deco = (*p)->deco[i];
        const operand *o = &ins.oprs[i];
        int64_t offs;

        output[slen++] = (colon ? ':' : i == 0 ? ' ' : ',');

        offs = o->offset;
        if (o->segment & SEG_RELATIVE) {
            offs += offset + length;
            /*
             * sort out wraparound
             */
            if (!(o->segment & (SEG_32BIT|SEG_64BIT)))
                offs &= 0xffff;
            else if (segsize != 64)
                offs &= 0xffffffff;

            /*
             * add sync marker, if autosync is on
             */
            if (autosync)
                add_sync(offs, 0L);
        }

        if (t & COLON)
            colon = true;
        else
            colon = false;

        if ((t & (REGISTER | FPUREG)) ||
                (o->segment & SEG_RMREG)) {
            enum reg_enum reg;
            reg = whichreg(t, o->basereg, ins.rex);
            if (t & TO)
                slen += snprintf(output + slen, outbufsize - slen, "to ");
            slen += snprintf(output + slen, outbufsize - slen, "%s",
                    nasm_reg_names[reg-EXPR_REG_START]);
            if (t & REGSET_MASK)
                slen += snprintf(output + slen, outbufsize - slen, "+%d",
                                 (int)((t & REGSET_MASK) >> (REGSET_SHIFT-1))-1);
            if (is_evex && deco)
                slen += append_evex_reg_deco(output + slen, outbufsize - slen,
                                             deco, ins.evex_p);
        } else if (!(UNITY & ~t)) {
            output[slen++] = '1';
        } else if (t & IMMEDIATE) {
            if (t & BITS8) {
                slen +=
                    snprintf(output + slen, outbufsize - slen, "byte ");
                if (o->segment & SEG_SIGNED) {
                    if (offs < 0) {
                        offs *= -1;
                        output[slen++] = '-';
                    } else
                        output[slen++] = '+';
                }
            } else if (t & BITS16) {
                slen +=
                    snprintf(output + slen, outbufsize - slen, "word ");
            } else if (t & BITS32) {
                slen +=
                    snprintf(output + slen, outbufsize - slen, "dword ");
            } else if (t & BITS64) {
                slen +=
                    snprintf(output + slen, outbufsize - slen, "qword ");
            } else if (t & NEAR) {
                slen +=
                    snprintf(output + slen, outbufsize - slen, "near ");
            } else if (t & SHORT) {
                slen +=
                    snprintf(output + slen, outbufsize - slen, "short ");
            }
            slen +=
                snprintf(output + slen, outbufsize - slen, "0x%"PRIx64"",
                        offs);
        } else if (!(MEM_OFFS & ~t)) {
            slen +=
                snprintf(output + slen, outbufsize - slen,
                        "[%s%s%s0x%"PRIx64"]",
                        (segover ? segover : ""),
                        (segover ? ":" : ""),
                        (o->disp_size == 64 ? "qword " :
                         o->disp_size == 32 ? "dword " :
                         o->disp_size == 16 ? "word " : ""), offs);
            segover = NULL;
        } else if (is_class(REGMEM, t)) {
            int started = false;
            if (t & BITS8)
                slen +=
                    snprintf(output + slen, outbufsize - slen, "byte ");
            if (t & BITS16)
                slen +=
                    snprintf(output + slen, outbufsize - slen, "word ");
            if (t & BITS32)
                slen +=
                    snprintf(output + slen, outbufsize - slen, "dword ");
            if (t & BITS64)
                slen +=
                    snprintf(output + slen, outbufsize - slen, "qword ");
            if (t & BITS80)
                slen +=
                    snprintf(output + slen, outbufsize - slen, "tword ");
            if ((ins.evex_p[2] & EVEX_P2B) && (deco & BRDCAST_MASK)) {
                /* when broadcasting, each element size should be used */
                if (deco & BR_BITS16)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "word ");
                else if (deco & BR_BITS32)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "dword ");
                else if (deco & BR_BITS64)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "qword ");
            } else {
                if (t & BITS128)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "oword ");
                if (t & BITS256)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "yword ");
                if (t & BITS512)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "zword ");
            }
            if (t & FAR)
                slen += snprintf(output + slen, outbufsize - slen, "far ");
            if (t & NEAR)
                slen +=
                    snprintf(output + slen, outbufsize - slen, "near ");
            output[slen++] = '[';
            if (o->disp_size)
                slen += snprintf(output + slen, outbufsize - slen, "%s",
                        (o->disp_size == 64 ? "qword " :
                         o->disp_size == 32 ? "dword " :
                         o->disp_size == 16 ? "word " :
                         ""));
            if (o->eaflags & EAF_REL)
                slen += snprintf(output + slen, outbufsize - slen, "rel ");
            if (segover) {
                slen +=
                    snprintf(output + slen, outbufsize - slen, "%s:",
                            segover);
                segover = NULL;
            }
            if (o->basereg != -1) {
                slen += snprintf(output + slen, outbufsize - slen, "%s",
                        nasm_reg_names[(o->basereg-EXPR_REG_START)]);
                started = true;
            }
            if (o->indexreg != -1 && !itemp_has(*best_p, IF_MIB)) {
                if (started)
                    output[slen++] = '+';
                slen += snprintf(output + slen, outbufsize - slen, "%s",
                        nasm_reg_names[(o->indexreg-EXPR_REG_START)]);
                if (o->scale > 1)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "*%d",
                                o->scale);
                started = true;
            }


            if (o->segment & SEG_DISP8) {
                if (is_evex) {
                    const char *prefix;
                    uint32_t offset = offs;
                    if ((int32_t)offset < 0) {
                        prefix = "-";
                        offset = -offset;
                    } else {
                        prefix = "+";
                    }
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "%s0x%"PRIx32"",
                                prefix, offset);
                } else {
                    const char *prefix;
                    uint8_t offset = offs;
                    if ((int8_t)offset < 0) {
                        prefix = "-";
                        offset = -offset;
                    } else {
                        prefix = "+";
                    }
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "%s0x%"PRIx8"",
                                prefix, offset);
                }
            } else if (o->segment & SEG_DISP16) {
                const char *prefix;
                uint16_t offset = offs;
                if ((int16_t)offset < 0 && started) {
                    offset = -offset;
                    prefix = "-";
                } else {
                    prefix = started ? "+" : "";
                }
                slen +=
                    snprintf(output + slen, outbufsize - slen,
                            "%s0x%"PRIx16"", prefix, offset);
            } else if (o->segment & SEG_DISP32) {
                if (prefix.asize == 64) {
                    const char *prefix;
                    uint64_t offset = offs;
                    if ((int32_t)offs < 0 && started) {
                        offset = -offset;
                        prefix = "-";
                    } else {
                        prefix = started ? "+" : "";
                    }
                    slen +=
                        snprintf(output + slen, outbufsize - slen,
                                "%s0x%"PRIx64"", prefix, offset);
                } else {
                    const char *prefix;
                    uint32_t offset = offs;
                    if ((int32_t) offset < 0 && started) {
                        offset = -offset;
                        prefix = "-";
                    } else {
                        prefix = started ? "+" : "";
                    }
                    slen +=
                        snprintf(output + slen, outbufsize - slen,
                                "%s0x%"PRIx32"", prefix, offset);
                }
            }

            if (o->indexreg != -1 && itemp_has(*best_p, IF_MIB)) {
                output[slen++] = ',';
                slen += snprintf(output + slen, outbufsize - slen, "%s",
                        nasm_reg_names[(o->indexreg-EXPR_REG_START)]);
                if (o->scale > 1)
                    slen +=
                        snprintf(output + slen, outbufsize - slen, "*%d",
                                o->scale);
                started = true;
            }

            output[slen++] = ']';

            if (is_evex && deco)
                slen += append_evex_mem_deco(output + slen, outbufsize - slen,
                                             t, deco, ins.evex_p);
        } else {
            slen +=
                snprintf(output + slen, outbufsize - slen, "<operand%d>",
                        i);
        }
    }
    output[slen] = '\0';
    if (segover) {              /* unused segment override */
        char *p = output;
        int count = slen + 1;
        while (count--)
            p[count + 3] = p[count];
        strncpy(output, segover, 2);
        output[2] = ' ';
    }
    return length;
}

/*
 * This is called when we don't have a complete instruction.  If it
 * is a standalone *single-byte* prefix show it as such, otherwise
 * print it as a literal.
 */
int32_t eatbyte(uint8_t *data, char *output, int outbufsize, int segsize)
{
    uint8_t byte = *data;
    const char *str = NULL;

    switch (byte) {
    case 0xF2:
        str = "repne";
        break;
    case 0xF3:
        str = "rep";
        break;
    case 0x9B:
        str = "wait";
        break;
    case 0xF0:
        str = "lock";
        break;
    case 0x2E:
        str = "cs";
        break;
    case 0x36:
        str = "ss";
        break;
    case 0x3E:
        str = "ds";
        break;
    case 0x26:
        str = "es";
        break;
    case 0x64:
        str = "fs";
        break;
    case 0x65:
        str = "gs";
        break;
    case 0x66:
        str = (segsize == 16) ? "o32" : "o16";
        break;
    case 0x67:
        str = (segsize == 32) ? "a16" : "a32";
        break;
    case REX_P + 0x0:
    case REX_P + 0x1:
    case REX_P + 0x2:
    case REX_P + 0x3:
    case REX_P + 0x4:
    case REX_P + 0x5:
    case REX_P + 0x6:
    case REX_P + 0x7:
    case REX_P + 0x8:
    case REX_P + 0x9:
    case REX_P + 0xA:
    case REX_P + 0xB:
    case REX_P + 0xC:
    case REX_P + 0xD:
    case REX_P + 0xE:
    case REX_P + 0xF:
        if (segsize == 64) {
            snprintf(output, outbufsize, "rex%s%s%s%s%s",
                    (byte == REX_P) ? "" : ".",
                    (byte & REX_W) ? "w" : "",
                    (byte & REX_R) ? "r" : "",
                    (byte & REX_X) ? "x" : "",
                    (byte & REX_B) ? "b" : "");
            break;
        }
        /* else fall through */
    default:
        snprintf(output, outbufsize, "db 0x%02x", byte);
        break;
    }

    if (str)
        snprintf(output, outbufsize, "%s", str);

    return 1;
}